Isolation of cellulose nanocrystals from rice husks using natural deep eutectic solvent

Cellulose nanocrystals (CNCs) are highly crystalline, rod-shaped nanoparticles derived from cellulose, commonly found in biomass such as rice husks. Rice husks, an agricultural waste rich in cellulose, can be utilized for CNC production. In this study, CNCs were isolated from rice husks using a natural deep eutectic solvent (NADES), an environmentally friendly solvent. The objective was to examine the effects of temperature and reaction time on CNC solubility during dissolution with NADES. The one-factor-at-a-time (OFAT) method revealed that the optimal conditions were at temperature of 120°C and a reaction time of 8 hours. Morphological analysis using microscopy showed that raw rice husks had a rough, solid, brown appearance, while alkaline-treated rice husks appeared smoother and more porous. Bleached rice husks exhibited a very smooth, white, and fluffy appearance, and CNCs appeared as transparent solids. Fourier transform infrared (FTIR) analysis indicated the presence of β-glycosidic linkages in all three samples (CNCs, alkaline-treated, and bleached rice husks), suggesting that the cellulose structure remained intact during pretreatment. Antibacterial activity was evaluated using the disc diffusion method, confirming that raw, alkaline-treated, and bleached rice husks, as well as CNCs isolated from rice husks, exhibited antibacterial properties against both gram-negative bacteria (E. coli) and gram-positive bacteria (B. subtilis). This study successfully isolated CNCs from rice husks using NADES, demonstrating the potential for further improvements to enhance production efficiency.